Apparatus for obtaining colored images



June 6, 1944. B T, HEW ON I 2,350,892

APPARATUS FOR OBTAINING COLORED IMAGES Filed Oct. 9, 1940 2 Sheets-Sheet l 4/ 4% K7 fi '91 4? 47 W4? lw I} 1 4/ W 3% pg/ (g fl 5ev+kqm Tom Hem/Son INVENTOK evJ/J June 6, 1944. -r wso 2,350,892

APPARATUS FOR OBTAINING COLORED IMAGES Filed Oct. 9, 1940 2 Sheets-Sheet 2 N ENrore Patented June 6, 1944 APPARATUS FOR OBTAINING COLORED IMAGES Bertram Tom Hewson, London, England Application October 9, 1940, Serial No. 360,354 In Great Britain May 30, 1938 1 Claim.

This invention relates to improved apparatus for obtaining colored images, and is equally applicable to color cinematography and color television, as will be more particularly described hereinafter. As applied to color cinematography, the chief object oi! the present invention is to provide a novel method of enabling color records to be obtained in a monochrome negative form on each and every frame of an ordinary cinematograph film which, when printed by the usual photographic methods in monochrome and projected in a suitable manner, will give a true rendering on the screen of all color values of the scene originally photographed. As applied to color television, the chief object of the present invention is to provide a simple apparatus by means of which the scene being televised can be reproduced in its true colors at the receiving end of the system.

All the apparatuses for color photography according to the present invention are equally applicable to color television. A system of color television will difi'er from a method of color cinematography only in so far that instead of making a visual record of the scene (the negative film), an electrical record is produced (the transmitted signals), and in that the record instead of being rendered available by means of a projected beam is made available by the conversion of the electrical impulses into a visual image.

The apparatuses for color cinematography according to the present invention employ normal procedur in exposure and projecting and normal film, and accordingly will be found to be equally applicable to color television. This extension of the present invention will be more particularly described hereinafter.

In order that this invention may be the more clearly understood, I will now proceed to describe the same with reference to the accompanying drawings, in which:

Figure 1 illustrates diagrammatically one form of electro-optical color filter device which may be used according to the present invention to split up the light both during exposure and pro- Jection.

Figure 2 is a view similar to Figure l illustrating a modified form of electro-optical color filter device according to the present invention, and

Figure 3 illustrates a modification of the device shown in Figure 2.

Figure 4 is a diagrammatic view illustrating the step of exposing the film and employing a still further modified form of electro-optical color filter device.

Figure 5 is a view similar to Figure 4 but illustrating the projection 01 the film.

Figure 6 is a diagrammatic view illustrating a modification of the electro-optical color filter device shown in Figures 4 and 5.

Figure 7 is a view illustrating a device for ensuring both vertica1 and horizontal registration of the film relative to the color filter device.

Figures 8 and 9 illustrate diagrammatically the application of the electro-optical color filter device shown in Figure l to the transmitter and receiver respectively of a television system.

Figures 10 and 11 are views similar to Figures 8 and 9 illustrating the application of the color filter-device shown in Figure 2 to a color television system, and.

Figure 12 illustrates the application of the form of color filter device shown ,in Figure 4 to the transmitter of a color television system.

Referring now more particularly to Figure 1 of the accompanying drawings, the electrooptical color filter device therein illustrated comprises a mount 40 in which are mounted polarising and analysing prisms or lenses ll, ordinary lenses 42 and, in the centre, the electro-optical device per so which consists of a device 43 capable of producing the bi-refrlngant phenomenon, for example, a Kerr cell, and also a color selecting crystal plate 44. The crystal plate 44 is efiectively a prism and is made of fiuorspar, Iceland spar or like crystalline substance which, when out at a given angle to the crystal axis, will pass only polarised light of certain wavebands and hence color according to the polarisation. As is well known, the angle at which the crystal is cut relative to the axis will determine the wavelength below which light is not transmitted by the plate, and, in carrying out the present invention, the angle is so chosen that a color adapted both to the spectral sensitivity of the light-sensitive film used and also to the characteristics of the Kerr cell II is passed.

The bi-refringant phenomenon above referred to occurs when high electrical voltages are applied to 9. Kerr cell or a substance such as nitrobenzene. The application of a high voltage to a Kerr cell appears to have the eflect of changing the nature of the polarised light passing through the same, the actual amount of change depending upon the voltage applied. Thus experiments have shown that a pencil of light impinging on a Kerr cell may be changed to green, yellow or even red light by the application of in Figure 1 is fixed in the gate of the camera and 5 suitable means (for example, a switch or rheostat driven by the camera) are provided for varying the voltage applied to the Kerr cell 43 from the source of supply 45 step by step over the whole of the necessary range whilst each successive frame ofthe film is being exposed to produce the sets of individual color records. Let us assume that the crystal plate 44 has been cut so that with normal polarisation it passes blue light and light of a higher wavelength. Now,

when the Kerr cell is so charged that it effectively passes the blue polarised light only the blue components of the incoming beam will be recorded whilst, when different electrical charges are applied to the Kerr cell, the nature of the light beam, presumably its polarisation, is changed so that the other color components, say green and red, transmitted by the crystal plate 44 are recorded on the light-sensitive film. A panchromatic film would be used in this as in all cases.

An identical device is used for projection, the same being disposed in identical relationship to the positive film as in the taking step for the reasons above set forth. The projected beam passing through the crystal plate 44 .will be, a 3

monochrome image but this will be correctly colored by operation of the Kerr cell under the infiuence of the various voltages applied to the same, these being synchronised with those used in the exposure stage. Registration of the films is obtained by means of the driving claws and registration marks on the films.

The device illustrated in Figure 1 may be used either way round in both the taking and the pro- Jecting steps, the same effect being obtained as will be readily understood.

The electro-optical color filter device illustrated in Figure 2 is similar to that illustrated in Figure 1, and like references have been used to indicate like parts. crystal plate 44 instead of, being stationary as in the construction illustrated in Figure 1 is adapted to be oscillated from image to image so as to cause the color selection thereof to vary from propriately by means of a flexible shaft i8l, are provided for rotating the crystal plate 44 intermittently or otherwise across the Kerr cell 43 from exposure to exposure.

This will cause the color selection image recorded on the film to vary from frame to frame as will be readily understood. A similar device, synchronously operated, is provided in the projection stage (see Figure 5), and like references have been used in this figure to indicate the corresponding parts to those shown in Figure 4.

A further modification of the electro-optical filter device according to the present invention is shown in Figure 6. This construction is similar to that shown in Figure 4, but the flexible shaft IBI, in addition to rotating the crystal plate 44, is also employed to rotate the polariser and analyser 4| relative to the crystal plate 44, for example, by means of the gearing illustrated diagrammatically at I82.

It will be appreciated that the satisfactory exploitation of the above described methods will depend on the accurate positioning of the image spaces relative to the color filter devices. This synchronisation may be effected by the perforations on the film acting on the claws 34 of which (as shown in Figure '7) there are preferably four engaging with the film both above and below the centre line of the gate aperture, and it is also preferable to provide means for ensuring lateral registration. Such means may comprise a blade spring 35 which bears on one side of the film to bias the same constantly to one side, the spring being provided with a central pin 36 housed in a suitable aperture in the gate 31.

As above stated, the present invention is also applicable to color television. The application of the system of color cinematography illustrated in Figure 1 to color television is shown in Figures 8 and 9. The television camera 90 is of the known form and is connected in the transmitter circuit (not shown) in the usual way. In front of the objective 9| of this television camera 90 is arranged the device illustrated in Figure 1, said In this case, howe er, the device functioning in exactly the same manner as described in connection with that figure. It will thus be seen that the actual image on the image plate 92 of the camera will be a colored image and, although the same may thus difi'er exposure to exposure. For this purpose, a cam 60 from the image produced on the exposed film in 80 driven appropriately by means of a flexible shaft Si is provided for oscillating the crystal plate 44 backwards and forwards across the Kerr cell 43 in order to vary the color selection from exposure to exposure. The function of the device (and also the counterpart device used in the pro- Jection stage) is the same as that described above in connection with Figure 1, the oscillation of the crystal plate serving to provide the desired color selection in conjunction with the Kerr cell.

Such an arrangement will permit a wider range of color selections to be obtained. In the modified electro-optical color filter device shown in Figure 3, the shaft 8|, in addition to rotating the cam 80 to oscillate the crystal 5 plate 44, is also employed to rotate the polariser and analyser ll, for example, by means of the gearing illustrated diagrammatically at 82. This again will enable a further adjustment to be made in the color selection.

case, means, for example, the gear I80 driven apthe corresponding cinematographic process, the difference is without effect since the electron beam is not selectively aifected by colors. The image transmitted 'will thus be a mosaic image and, if a corresponding device to that shown in Figure 1 and operated synchronously in a like manner be installed in front of the cathode ray 'oscillograph 96 as shown in Figure 9, the same effect as is obtained when projecting with the system of colorcinematography hereinbefore described will be obtained.

In the like manner it is possible to apply the other systems of color cinematography to corresponding color television systems, as will be appreciated on reference to Figures 10 to 12 of the accompanying drawings. Figures 10 and 11 show respectively the application of the-color cinematograph system of Figure 2 t0 the transmitter and receiver of a color television system. In like manner Figure 12 illustrates the application of the device shown in Figure 4 to a color television transmitter. In allthese figures illustrating the application of the present invention to color television, like reference numerals have been used to indicate the corresponding parts shown in the like figures oi the color cinematography systems. Since the operation of the devices is the same when applied to color television as when applied to color cinematography (as explained above) further description of these color television systems is deemed to be unnecessary.

The expression electro-optical color filter device used herein connotes a system of one or more lenses or prisms together with electrical means which, although themselves uncolored, are adapted to filter out certain wavebands from a beam of light to produce individual color selection images or mosaic screen images similar to those usually employed in color cinematography. The expression producing a further image from the image thus produced used in the claims is intended to cover, in the case of color cinematography, the usual optical or contact printing of the positive from the negative and, in the case of television, the steps of transmitting the image produced in the camera and the making of the same visible at the receiver in the usual way.

It will be appreciated that if the television.

camera be regarded as the photographing camera and the image producer at the receiver be regarded as a combination of the projector and the positive film, then all that has been described above in connection with color cinematography will be equally applicable to a system of color television.

An absolutely perfect spatial registration of all the color elements or similar parts in the successive images may result in a constant division line between the elements which may give rise to a troublesome eflect in the projected or viewed 35 image. In order to avoid this possible disadvantage, the present invention also envisages the possibility of so moving the filter elements that the division lines do not remain constant but vary from image to image whereby no hard and fast demarkation occurs.

Many modifications of the particular arrangements above will be apparent to those skilled in the art and such modifications may obviously be carried into practice without departing from the scope of the present inventionas defined in the appended claim. For example, the whole gear may be thrown out of operation to produce images in black and white instead of colors, and againfit will be appreciated that the system is particularly applicable to combined cameras and projectors since the one filter device is applicable to both purposes.

I claim:

In a device for producing or reproducing a cinematographic succession of multi-monochromatic images of a niulti-colored object on or from a separate image recording element, the combination of two cooperating optical filter elements arranged to be passed successively by a stream of polychromatic light, one of said optical filter elements being a light polarizing unit and the other optical filter element comprising a composite color filter plate consisting of several sets of difierently out small cry stal elements, each set passing a different monochromatic color of a polarized stream of polychromatic light, an electrical filter element comprising a Kerr cell disposed adjacent said color filter plate, means to apply a voltage to said Kerr cell, means to vary said voltage between successive images, and means to effect between successive images a movement of at least one 01 said optical filter elements in a plane at right angles to its optical axis and adapted to cause a relative displacement between the two optical filter elements from image to image.

BERTRAM TOM HEWSON. 

